Such transducers are known from EP-A-0851710 and find application especially in hearing aids.
For the proper functioning of such a transducer, various requirements are imposed on the construction of inter alia the diaphragm. On the one hand, the diaphragm must be able to move freely, on the other hand it is, of course, necessary to secure the diaphragm somehow. It is therefore customary to attach the diaphragm by its circumferential edge to a support frame or to the case, whereby the central portion of the diaphragm remains unattached in order to be able to vibrate. Often, between this central diaphragm portion and the edge portion, a transition portion formed as a groove or bellows is included to give the central diaphragm portion as much freedom of vibration as possible.
From EP-A-0851710, it is also known to attach the diaphragm to a film, which film is attached to the case. To this end, the film is folded to enable free movement of the diaphragm. A complete suspension of the diaphragm is necessary to obtain a proper acoustic separation between the volume in the transducer above and under the diaphragm.
From GB-A-2229339 also an electroacoustic transducer with a case comprising a diaphragm produced on a film is known. Around the outer edge of a central diaphragm portion a free strip of film is present. The circumferential outer edge of this film is bended at a right angle with respect to the plane of the central diaphragm portion and the bended portion is glued to the inner wall of the case. As described in EP-A-0851710 this manner of connecting has certain disadvantages.
As already mentioned, an acoustic transducer is applied in, for instance, hearing aids, intended to be positioned in the exterior auditory canal of a person. Hence, there is, within this technical field, a continuous pursuit of ever increasing miniaturization, demanding a great sensitivity of the various applied parts.
Apart from this pursuit of miniaturization, it is desired to enlarge the volume displacement by the diaphragm as much as possible, to which end it is desired that the central diaphragm portion be as large as possible. Additionally, it is desired to keep the costs of manufacturing the construction of the diaphragm as low as possible by applying as few parts as possible.
A drawback of all hitherto proposed manners of connecting a diaphragm to the case is the necessity of different production steps, each involving the possible occurrence of errors, which sometimes can and sometimes cannot be corrected, but always entail additional activities and hence additional costs.